Broadcom wireless cards are known to have compatibility issues in Linux systems, and this tag should be used for questions about getting wireless working well on Ubuntu when a Broadcom card is involved. Installing additional drivers or adjusting configurations can usually resolve issues. Please check your hardware and search for related questions, and include all relevant information when posting.
Broadcom is a company that produces hardware devices, notably wireless networking cards that have historically been troublesome for Linux users. Devices have a name starting with "BCM".
Before asking, please have a look at the canonical question Installing Broadcom Wireless Drivers to see if this solves your issues.
The relevant drivers are
wl(restrictively licenced driver from Broadcom)
b43(reverse-engineered open source driver)
brcmfmac(new open source drivers from Broadcom)
Networking issues are hardware specific, so please give relevant information when asking. The output of
lspci -knn | grep -iA2 net usually helps. You can also use the Wireless Info script.